Steam turbine designs generally include static nozzle segments that direct air flow into rotating buckets that are connected to a rotor. In steam turbines, the nozzle (airfoil) construction is typically called a diaphragm stage. The diaphragm is supported vertically by several methods at a horizontal joint. Typically, the vertical supports may be support bars, pins or support screws. Each design has some advantages and disadvantages.
One design may include a pin at or near the horizontal joint. This design typically would be used in low pressure (LP) turbines where there is more accessibility to get at the pin (between the hood and the inner casing). This design generally cannot support as much weight as a typical support bar design. This design also requires that the pin be removed for machining the required adjustment. This design also requires that the diaphragm be supported during this operation. An eccentric pin also could be used but the added complexity may be cost prohibitive.
Another design is a “bolted diaphragm” support bar design that requires the diaphragm be installed for measurement. The diaphragm and rotor then are removed so the support bar can be machined to adjust the vertical position of the diaphragm. The sequence is then repeated to verify the position and repeated again if necessary. The support screw designs can only be used on the smaller high pressure (HP) stages because the weight may be too great on the intermediate pressure (IP) and low pressure (LP) stages. One drawback to the support screw design is that there is not enough space in the diaphragm cross section to allow for bolting the upper half diaphragm to the lower half diaphragm. This non-bolting creates a situation in which a gap is created between the upper and lower half diaphragms at the horizontal split line. This gap causes efficiency losses within the steam turbine.
Therefore, the support bars currently used require the removal of the diaphragm and rotor for adjustment. It may take several shifts or days to adjust, as both the diaphragm and the rotor must be removed to make the adjustment. Also, support screw designs are used for smaller HP stages where the weight is low enough to allow the design to work. The support screw concept does not allow for bolting the upper and lower half diaphragms, which is desirable.
Therefore, there is a need for a support bar type design that has the ability to support the diaphragm of the steam turbine, and be adjusted quickly without modification to the hardware.